The invention relates to the manufacture of continuous length troughs and more particularly to an improved drainage trough assembly and method of injection molding continuous length ribbed plastic drainage troughs of the type used in the handling of fluid run off in ground level applications.
Drainage troughs, are in common use for collecting and distributing ground level run-off of fluids, such as storm water, waste fluid spills, and various cleaning and drainage applications. Generally such troughs are installed at or formed just below ground level in a paved area and the arrangement comprises a screen, grate or the like which covers the trough to enable vehicles, pedestrians and/or large objects to pass thereover without falling into the trough, while allowing fluids to pass through.
Pre-manufactured troughs have been generally available, formed from a rigid metal or plastic, typically by extruding or casting same to a desired length or various standard lengths. To protect against crushing, such troughs are generally sturdily manufactured and thus are difficult to cut into variations from standard lengths. In recent years, there has been a desire to manufacture and use extruded plastic troughs in place of metal troughs for both corrosion resistance and ease of handling, however the wall thickness required to produce a suitably crush resistant plastic trough is significant and thus material costs are expensive. To reduce costs, a plastic trough of lesser wall thickness has been proposed which is formed with a plurality of circumferential supporting ribs. The support ribs enable support of a weight supporting grate and provide suitable resistance against crushing the form of the trough, but the presence of the ribs generally are problematic to the convenient manufacture of the trough by extrusion. Thus, the manufacture of troughs by injection molding is not particularly desirable in that multiple distinct molds are generally necessary to enable the manufacture of the various standard sizes and lengths for general availability, and variations from such standards generally require the creation of additional expensive molds.
U.S. Pat. No. 3,992,503 discloses a method of manufacturing continuous ribbed pipes from thermoplastic materials, wherein a section of pipe is formed by injection molding, the section is allowed to set in the mold, the set pipe casting is ejected from the mold, an end of the set pipe casting is reset into an open end of the same mold, and further molten thermoplastic material is injected into the mold. The molten thermoplastic material engages against the end of the reset pipe casting, and is said to fuse with the thermoplastic material at the end of the reset pipe, with repetition of the operation resulting in the formation of a continuous molded pipe of welded sections. Provisions are made in the patent for a heating wire located at the open end of the mold to surround the reset end of the pipe and soften it to enable welding of the sections, and/or for the pipe to comprise a stepped diameter at the ends to facilitate softening of the thermoset resin to form a weld among the sections.
The disclosure of U.S. Pat. No. 3,992,503, makes it apparent that the final product being manufactured merely comprises a continuous length of thermoplastic pipe formed from a plurality of sections which have been welded together using conventional welding means, and thus having the inherent seam weakness of thermoplastic welds.
It is an object of the present invention to provide a method of manufacturing injection molded, continuous length troughs having suitable ribbed supports integral therewith.
It is a further object of the present invention to provide a method of injection mold manufacturing of troughs, which enables a homogeneous continuity of thermoplastic material throughout its length.
It is another object of the present invention to provide a novel injection mold formed drainage trough, having integrally molded raised ribs and support attachment elements.
It is still another object of the present invention to provide a novel drainage trough system enabled for rapid and convenient installation in diverse environments.
These and other objects of the invention will become apparent from the following recitation of the invention.
The present invention comprises a method of manufacturing a continuous length trough, comprising spaced, raised integral ribs, from thermoplastic resin material, comprising the steps of: (a) providing an injection mold cavity arranged between mating male and female molds, said cavity being shaped to form an elongate section of a trough having spaced, outwardly raised ribs, said cavity being open at a first end and closed at the opposite end, said opposite end of said cavity being configured to form a plurality of spaced extensions arranged along an end of a formed trough section; (b) providing means for removably covering the open first end of said mold cavity; (c) providing means for cooling a molten thermoplastic resin comprised in said cavity; (d) covering said first end of said mold cavity and injecting a molten thermoplastic resin, at an elevated temperature, into said cavity between said male and female molds; (e) cooling said molten thermoplastic resin to a pre-determined resin setting temperature; (f) uncovering said first end and removing a molded resin-set trough section from the female and male molds; (g) inserting the opposite end of said resin-set trough section, comprising the spaced extensions, into the open end of the mold cavity sufficient to close the open end of said mold cavity; (h) injecting molten thermoplastic resin into the mold cavity, at an elevated temperature sufficient to melt said spaced extensions of said first resin-set trough section and form a continuing section of trough, homogeneous with said first trough section; (i) cooling the molten thermoplastic resin to a pre-established setting temperature; (j) removing the molded second trough section from the female and male molds; and repeating steps (g) through (j) in successive order until a trough of a desired length is formed.
In a preferred embodiment, the elongate mold cavity in an injection molding process is formed by the confluence of three or more components. Thus, in a particularly preferred arrangement an elongate male mold, having an exterior surface configured to form the generally trough shaped configuration of an interior surface of a molded trough, is juxtaposed between two or more generally opposing female molds with the cooperative engagement of the three or more components forming the cavity to be injection filled, and the formed product is released from the mold cavity by disengagement of the three or more components. In a preferred operating arrangement between three components, a female mold is fixed in position and the male and another female mold are arranged to move toward and away from the female mold. Thus, in a preferred molding cycle, the female mold is arranged in a generally stable position, while a male and female molds are arranged in generally opposing relationship to the female mold and are enabled to be moved from a first position spaced from the stable female mold to a second position surrounding the male mold and defining the mold cavity. When moved to the second position, the female molds generally engage each other and the male mold, forming a sealed mold cavity surrounding about the length of the elongate male mold. The mold cavity is then injected with a suitable plastic composition; the injected plastic composition is allowed to cool to at least initiate setting thereof, with or without cooling assist; and upon the plastic composition reaching a suitable setting point, the male and movable female mold are withdrawn from the second position toward the first position.
Such arrangement of male and female molds enables the convenient formation of diverse integrally molded structures on the exterior surface of the molded trough, such as raised ribs and/or other protruding integral structural elements and the like, without the mold release problems associated with prior art arrangements.
In a preferred arrangement wherein two female molds engage the male mold from opposite legs of the generally trough shape, the generally opposite directional movement of the female molds away from the male mold toward the second position, provides an assist to release of the molded product from all three confluent molds. It has been found that moving the female molds in opposite directions away from the male mold, typically results in a loose molded product laying without problematic adherence on the male mold. It is believed that the initial incremental opposing movement of the female molds away from the male mold causes an initial flex to the molded product which breaks the surface adherence of the molded product to the male mold, and the resistance of the body of the molded product to further flex because of the engagement of opposite sides of the molded product against the structural trough shape of the male mold breaks the surface adherence of the molded product to the female molds. The result is the release of a molded product without the usual need for critical release agent parameters.
In addition to raised ribs, the exterior side walls of the trough may comprise integrally molded projecting tabs, surfaces, support configurations, bracket attachment elements and the like, which generally extend from the exterior sidewall of the trough to provide stabilizing, support and/or attachment elements for maintaining the integrity of the shape and positioning of the trough in its constructed installed environment.
In one embodiment, raised molded structures can be conveniently formed on the exterior surface of the trough to enable the convenient attachment of other support framework, structures, spacers and the like which may enable the leveling of the trough during installation and maintaining the trough in position during use. In a still further embodiment, the exterior surface of the trough of the invention comprises integrally molded slots, depressions, hollows and/or the like for convenient attachment of one or more support bracket(s) during installation, the support bracket(s) being configured to support the trough at a defined level from the supporting under-surface of a trench and the like to enable the pouring of concrete and the like around the trough to assure convenient integral installation of the trough along a finished formed floor and the like.
In a preferred embodiment of the mold cavity, the end of the mold cavity opposite the open end of the mold cavity comprises a primary rib cavity, configured to form a molded integral primary raised rib in the formed trough proximate the plurality of spaced extensions. Similarly, the mold cavity proximate the open end comprises a secondary rib cavity, configured to form a integral raised secondary rib in the formed trough, the configuration being sized and dimensioned to matingly engage the primary raised rib upon re-positioning. The location and configuration of the primary and secondary rib cavities is to enable repositioning of a released molded trough section in the mold cavity with the primary raised rib of the molded trough repositioned in the secondary rib cavity with the spaced extensions protruding inwardly of the mold cavity. Such configuration of a raised rib cavity in the general mold cavity proximate the open end of the mold, provides a convenient operational seal to resist resin leakage from the open end during manufacture of continuous length molded trough.
In general, the mold cavity may be configured with any desirable plurality of integral raised rib cavities along the length of the general mold cavity. In a particularly preferred embodiment, integral raised ribs are molded in closely spaced pairs. For example, the secondary rib cavity can comprise a pair of closely spaced rib cavities and the primary rib cavity a single rib cavity, such that upon repositioning and re-injection, the continuum of material can be positioned to occur along the trough at a rib and/or between two closely spaced ribs. In further example both the primary and secondary rib cavities can comprise closely spaced rib cavities or a single rib cavity and the continuum can be positioned to occur adjacent to the rib on the formed trough. In still further example closely spaced pairs of ribs may be comprised anywhere along the length of the trough, with the primary and secondary rib cavities arranged to form single rib embodiments.
The method of the invention enables the formation of closely spaced raised ribs flanking the seamless melding of resin material at the continuum of the molded trough and/or at standard measured lengths along the trough, providing a convenient end point(s) for cutting measured standard trough lengths and/or attaching convenient accessories. Thus, for example, the mold cavity can be configured to a standard length for example a one or two foot length, with repeating closely spaced ribs arranged at standard lengths, as for example 6 inch lengths, so that the trough can be conveniently formed at long lengths for storage and conveniently cut to convenient increments for use and/or custom length sale.
In a preferred configuration of the trough of the invention, the mold cavity is configured to provide pairs of closely spaced ribs arranged at standard measured increments along the length of the trough, and/or integrally molded snap receivers configured to receive and engage supporting elements, and/or integrally molded stabilizing tabs and the like. In one configuration, supporting elements are configured in the general trough shape and are arranged to insert into a slot formed by a pair of closely spaced ribs, gripping the trough and providing a secure pedestal for holding the trough at a desired height and placement within a trench. In another configuration, the trough may further contain integrally molded receivers and the like, configured to engage mating snap elements of a support member and the like which similarly engage the trough to provide a secure pedestal or the like for convenient installation.
The configuration and dimensioning of the spaced extensions arranged along the opposite end of the trough is critical to the formation of a homogeneous continuum of thermoplastic material in the process of the invention. Applicants have found that in the manufacture of troughs having a wall thickness in a non-ribbed portion of the trough of about ⅝xe2x80x2 or less, extension configurations in the form of distinct spaced elongate fingers having generally parallel sides and a rounded tip is generally preferred, wherein the spacing between such formed fingers is generally dimensioned to be about the width of such formed finger, and the thickness of such finger is about half the wall thickness. Thus, wherein the non-ribbed wall thickness of the molded product is about {fraction (3/16)}xe2x80x2 a preferred finger is about {fraction (3/16)}xe2x80x2 wide, about xc2xdxe2x80x2 long and about {fraction (3/32)}xe2x80x2 thick, with the distance between fingers being about {fraction (3/16)}xe2x80x2. In one embodiment one side of a finger is coplaner with one surface of the wall with the other side of the finger being offset from the opposite surface of the wall. In a preferred embodiment, both sides of the finger are offset from about the planes of both surfaces of the wall.
The arrangement of the fingers, together with the method of the invention enables a surprising continuum of material at the boundaries of a trough section, providing a homogeneity which does not appear to be achieved by conventional welding techniques of the prior art.
A primary use of molded troughs of the invention is as a terminus for fluid flow from a pitched surface and the like, the arrangement intended to drain fluids from a surface toward the trough and the trough intended to collect and/or redirect the flow of such fluids draining to it as may be desired.
In a preferred use, the installation of drainage troughs is generally performed integral with the construction of a contiguous surface such as a poured concrete and/or cement slab with the trough comprising a grate the installation being sufficient to support significant weight, for example a vehicle passing thereover. In such use of a plastic trough, it is generally critical that the trough be integrally supported through its length and be appropriately aligned and leveled in reference to the contiguous surfaces. Prior art methods of installation includes the use of support materials such as stone, sand, dirt and the like to generally align, level and support the trough during construction, with rods pins, wiring and the like being used to hold the trough in place during the pouring of concrete and the like materials. Such method of installation is time intensive, generally requiring two or more workers propping up the trough from a supporting under-surface to appropriate finished concrete level and alignment and thereafter carefully pouring surrounding concrete and the like to maintain the alignment of the trough through the formation and leveling of the surrounding surfaces. Additionally, in most installations it is generally desired to provide an appropriate outlet(s) from the trough and drainage pipes connecting the outlet(s) to a further location. The combination of rigging supporting arrangements for the trough, outlets and associated piping and maintaining the level of the rigged arrangement during pouring of a fluid concrete slurry or the like, as the trough tends to float upwardly, significantly increases the amount of adjustment, complexity and time required to complete the installation.
The trough and system of the present invention significantly reduces the problems and time associated with installation by providing conveniently pre-mountable base supported trough brackets, which are generally molded from the same material as the trough and are designed such that their support base rests on the supporting under-surface, to hold the trough and accompanying outlet(s) at a defined level spaced from the supporting under-surface to enable easy completion of piping and convenient under-surface preparation. Thus, preparing the site for positioning a trough system of the invention contiguous with a poured concrete and/or the like slab, merely requires preparing an appropriate under-surface beneath the trough on which the support brackets rest, which is adjacent to and/or contiguous with the suitably leveled under-surface on which the concrete slab and the like is to be poured. The spacing between the base of the brackets and the bottom of the trough is dimensioned to allow convenient attachment of appropriate piping to one or more outlets comprised in the trough. Though not generally required, the base of the brackets may be conveniently pinned and/or rodded to the under-surface, and/or stone, sand, dirt or the like may be placed on the base of the brackets to maintain the alignment of the trough in place during pouring of the concrete.
In a typical poured concrete installation, the brackets need not be pinned and/or rodded to the under-surface to maintain the trough in its leveled and/or aligned position. Instead, the bracket supported trough is arranged so that the base of the brackets rest on the under-surface, an amount of concrete or the like is initially poured on and around the base of the brackets, sufficient to steady the trough in level and/or alignment, and the mass of initial poured concrete surrounding the base end of the brackets is sufficient to maintain the trough from floating and/or moving as the level of poured concrete is raised to surround the exterior surface of the trough. Indeed, it is not unusual that the supporting under-surface is only roughly leveled and/or aligned for the trough such that initially the trough is only generally aligned and leveled and final critical alignment and leveling is not done until an initial level of concrete is poured which surrounds the base of the brackets, the final alignment of the trough being done by moving the brackets in the concrete slurry such that once aligned and leveled further concrete is added under the supported trough and evenly around the sides of the trough to the desired level of the contiguous surface. The covering of the base of the brackets by the concrete mass is generally sufficient to prevent the trough from floating.
Various thermoplastic materials may be used in the process of the invention, including resin compositions comprising a filler and/or reinforcing material. An important element to the method of the invention is the selection of a thermoplastic resin and/or resin composition that has a broad enough setting temperature range so that plasticity of the extension containing opposite end of the molded portion of trough is retained for a time sufficient to enable removal of the molded portion from the mold, reinsertion of the opposite end of the molded portion into the mold cavity and injection of thermoplastic resin into the mold cavity. Thus, the resin/composition at the opposite end of the trough has not reached a hardened set before the injection of further molten resin forming the continuum of the trough, but has retained plasticity.
Generally, a convenient means for determining the suitability of the setting temperature range of a resin/composition in the method of the invention is by observation of the amount of shrinkage the molded trough experiences as it cools from its molten state to its hardened state. As plasticity decreases during setting of the resin/composition, the molded product shrinks from a larger molten volume to a smaller solid. e.g. hardened, volume. Some degree of setting must occur before the product is removed from the mold to insure structural integrity of the trough section during handling. Ideally, the less shrink that occurs before the product can be removed, reinserted and resin/composition injected, the higher the probability of attaining a homogeneous continuum at the interface.
Generally, it has been found that the setting resin/composition product has undergone a sufficient reduction in structural plasticity to enable removal of the product from the mold, without compromising structural integrity, if the molded product has shrunk to about 5% of its anticipated shrinkage to a hardened state. Generally also, the process of the invention provides a continuum of homogeneous material at the interface of the opposite end and newly injected molten resin if the plasticity of the opposite end has not been so reduced that the product has shrunk more than about 90% of its anticipated shrinkage to a hardened state.
Thus, convenient determinations of the suitability of the setting temperature range of a resin/composition for use in the process of the invention, can be made by measuring the shrink time necessary for a molded product to go from about 5% of its total shrink to hardness, to 90% of its total shrink to hardness under the temperature conditions of the environment surrounding the opening of the mold, removal and reinsertion of the opposite end, closing of the mold and injection of new molten resin/composition. Comparison of this time to the processing time necessary to effectively do same, confirms the suitability or not of the resin/composition. Preferably, the processing time falls within about 5% of shrink or less to about 75% of shrink of the resin/composition, and more preferably within about 5% of shrink or less to about 50% of shrink of the resin/composition.
In a preferred embodiment of the invention, the thermoplastics material comprises a suitable polyvinyl, polystyrene or acrylate resin, such as a suitable polymerized olefin or a copolymer with styrene. Particularly preferred is polypropylene, most preferred being a generally non-filler comprising polypropylene.
By way of example, preferred embodiments of the invention will be described with reference to the accompanying drawings.